This invention relates to a point-to-multipoint communication network, which is alternatively called a multicast communication network or otherwise.
Various point-to-multipoint communication networks are known. For example, a point-to-multipoint communication network is disclosed in Japanese Patent Prepublication (Kokai) No. 96,542 of 1981 for a Patent Application filed in Japan by International Business Machines Corporation based on a United States Patent Application which matured into U.S. Pat. No. 4,285,064 on Sep. 28, 1979. Another point-to-multipoint communication network is revealed in Japanese Patent Prepublication No. 103,339 of 1986. Still another point-to-multipoint communication network is described in a paper contributed by Tomoki Ohsawa and Seiji Kachi, the present joint inventors, and three others under the title of "Computer Mesh Network Using Satellite: COMNUS" to the COMSOC Technical Committee.
In the manner which will later be described more in detail, a point-to-multipoint communication network basically comprises a hub station and a plurality of satellite stations. The hub and the satellite stations are connected together by a communication medium which typically includes a transponder on board an artificial satellite.
The hub station may serve as a transmitting station and the satellite stations, as receiving stations. Data are transmitted as a multicast or broadcast signal from the transmitting station to the receiving stations through communication channels established through the communication medium. Receiving the multicast signal, each receiving station may send an acknowledgement signal back towards the transmitting station. The point-to-multipoint communication network therefore comprises a multicast communication arrangement for establishing the communication channels between the transmitting station and the receiving stations for use in transmission of the multicast signal.
It should be noted in this connection that the receiving stations are not always capable of correctly receiving the multicast signal. This is because a certain one of the receiving stations may be either still kept in an inoperative state or unexpectedly involved in trouble. In this manner, at least one of the receiving stations may be a failing or unsuccessful station that fails to duly receive the multicast signal.
It is possible for the transmitting station to confirm reception of the multicast signal by the receiving stations by receiving the acknowledgement signals from the receiving stations. It has, however, been impossible with a conventional point-to-multipoint communication network to administrate the failing station or stations and to again transmit the multicast signal to the failing station or stations.